Guide
How Satellites Detect Wildfires: A Plain-Language Guide to Thermal Hotspots
By the GlobalRisk team · Published 2026-10-06
Fire layers on a map, including those on GlobalRisk, are built from thermal hotspots detected by Earth-observing satellites. NASA distributes them through FIRMS, the Fire Information for Resource Management System, and they are used by fire agencies and researchers worldwide.
How detection works
Instruments such as MODIS and VIIRS measure infrared energy radiating from the ground. A fire is much hotter than its surroundings, so the sensor sees a pixel that is unusually bright at certain infrared wavelengths. Software compares each pixel with its neighbors and flags those that are anomalously hot. Each flagged pixel becomes a "hotspot" with a location, time, and an estimate of fire radiative power.
What a hotspot is, and is not
- A hotspot marks a pixel roughly 375 meters to 1 kilometer across, depending on the instrument, that contains a heat source. It is not a precise fire perimeter.
- One large fire usually produces many hotspots; a single hotspot may be a small fire.
- Not every hotspot is a wildfire. Agricultural burning, gas flares, industrial heat sources and some volcanic activity can also be detected.
How fresh is it?
Polar-orbiting satellites pass over any given location a few times per day, so a fire can burn for hours before it is seen. Data is typically available within about three hours of observation in "near-real-time" products, then refined later. Heavy cloud cover and thick smoke can hide fires, and very small or short fires may be missed entirely.
Reading fire data responsibly
- A cluster of hotspots in a forested area during a dry season is a stronger signal than an isolated point in farmland.
- Use hotspots to see where fire activity is detected, not where it is not. Missing hotspots do not prove an area is safe.
- For evacuation notices and fire perimeters, rely on your local fire or emergency authority.
Fire and other natural events also appear in recent events and on country pages. For the other feeds we use, see the methodology.
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General information only, not professional or emergency advice. Our methodology · Browse by country